On Feb. 9, 1988, U.S. Pat. No. 4,724,400, entitled "Linear Amplifier" was issued in the name of G. G. Luettgenau to TRW Inc. (the "400 patent"). Such patent is treated herein solely as a publication.
The '400 patent shows and describes a microwave splitter-combiner apparatus comprising a cylindrical stack of vertically superposed circular metallic plates defining within the stack an upper divider waveguide or cavity and a lower combiner waveguide or cavity. Each such cavity comprises a pair of vertically spaced metallic walls and a chamber between and bounded by such walls and providing a passage through which microwaves propagate, the chamber being essentially in the form of a horizontal cylindrical disc. In the divider waveguide, the microwaves travel through its cylindrical disc chamber from its center radially outward while, in the combiner waveguide, such travel in its chamber is radially inward towards the center of the chamber. Both of the cavities have metallic wall portions bounding the cavity in which are concentric ridges and valleys formed by milling of a thick plate providing that wall surface.
Disposed on a plate member providing a top closure for the mentioned stack is a set of twenty r.f. amplifier operating units. The twenty units are equiangularly spaced in carousel fashion around the top of such member in respective radial planes which are vertical and pass through the vertical axis of the stack.
Each of such twenty r.f. amplifier units is coupled to the splitter waveguide by an input coaxial connector and to the combiner waveguide by an output coaxial connector. In the operation of the apparatus, high frequency electromagnetic energy is fed to the splitter waveguide's center, travels therefrom radially outward through the waveguide's chamber to the twenty input connectors and is then fed upward by them to the twenty amplifiers which operate in parallel to amplify such energy. The amplified energy is then fed via the twenty output connectors to points in the combiner waveguide's chamber which are radially outward of the chamber's center. From those points the energy travels as waves radially inward through the chamber to its center to there be combined and provide an amplified output from the apparatus.
In the apparatus of the '400 patent, the divider and combiner cavities are bounded on the upper side of the upper cavity and the lower side of the lower cavity by respectively, a relatively thick rigid top metal closure plate and a similarly thick rigid bottom closure plate. The two cavities have between them a single central intermediate relatively thick rigid metal plate providing both the bottom closure wall for the upper cavity and the top closure wall for the lower cavity. That central plate is milled on its top side to provide concentric ridges and valleys facing towards the upper cavity. The bottom closure plate is similarly milled on its upper side to provide concentric ridges and valleys facing towards the lower cavity.
In co-pending U.S. patent application, Ser. No. 07/472,160, now U.S. Pat. No. 5,032,798 entitled "Improved Cavity Means For Microwave Divider-Combiner Units", filed Jan. 30, 1990 in the name of Robert E. Myer, one of the co-inventors hereof, and assigned to the assignee hereof, embodiments of microwave divider-combiner units are disclosed in which, in contrast to the '400 patent, unmilled metal plates are used to provide both the top metal closure wall for the upper cavity and the bottom metal closure wall for the lower cavity. As a further distinction from the '400 patent, the single central plate of that patent is replaced by two sheet metal plates which provide, respectively, the bottom and top metal walls bounding, respectively, the upper and lower cavity. In each of these sheet metal plates, the metal thereof is inflected by stamping or the like to form in such bottom and top walls respective sets of concentric ridges and valleys facing away from each other and towards the cavities bounded by such walls.
While these embodiments avoid the high milling costs of the plates used for the structure of the '400 patent and provide other advantages, the coaxial connectors in such embodiments which pass from the amplifiers to the lower cavity are of a length which desirably could be shortened. Moreover, even with the advances in the art provided by such embodiments, room remains to further lower the cost of fabricating the cavity closure structure.